Snap, Crackle, and Pop!

The Venus flytrap is a marvel of engineering. In a fraction of a second, without the aid of nerves or muscles, the carnivorous plant can snap closed on an insect. But since Charles Darwin first saw the flytrap in the 19th century, scientists have been puzzled by how it works. An international team of mathematicians, engineers, and biologists has found out.

The answer, says Lakshminarayanan Mahadevan, Harvard University professor of applied mathematics and mechanics, is simple physics. When open, the plant’s trap leaves are not unlike half a tennis ball turned inside out. They are apparently held in tension by water pressure and, like the tennis ball, will snap back into their original shape with dramatic speed. When an insect happens into the plant’s trap zone, it triggers minuscule hairs that send a tiny electrical signal, causing small amounts of water to shift. That releases the tension on the curved leaves, which immediately clamp shut.

The team painted tiny fluorescent dots on the flytrap’s leaves and then videotaped it in action with a high-speed camera. That way they could reconstruct the shape of the leaf instant by instant and build a computer model showing the process. Still unknown is how the flytrap changes water pressure inside the leaf so quickly. And, so far, there are no practical applications for this knowledge.

But applying the findings was not the point, says Mahadevan, who has also studied such seemingly mundane topics as the fault lines in crumpled paper and why honey coils when poured. “We started looking at the plant because it is such a fantastic piece of natural engineering,” he says. “Even Darwin was puzzled that something like this could have evolved. The thing even has a built-in false-alarm protector; you’ve got to trigger the hairs twice within a certain period of time. It’s one of those things that makes you really respect the powers of evolution and nature.”